1. Field of the Invention
This invention relates to compacted rare earth-iron-boron particle magnets that are produced by a novel process whereby the magnetic particles are protected from oxidation during and after manufacture to create a durable, flux-loss resistant permanent magnet.
2. Description of the Prior Art
Recently a novel family of magnetic alloys with enhanced permanent magnetic strength have been disclosed. These alloys are based on light rare earth elements (RE), specifically neodymium and praseodymium, the transition metal element, iron, and boron. This material and a method of manufacturing bonded magnets from it are disclosed in U.S. Pat. No. 4,558,077 and the U.S. Pat. applications disclosed therein. These magnetic alloys have been marketed under the trade name "MAGNEQUENCH".
It is well known that the magnetic particles produced by the above-referenced process have a large surface area per unit volume and are of a composition that is reactive to ordinary atmosphere. Moreover, it is known that when these magnetic particles are exposed to the atmosphere they are oxidized, irreversibly decreasing the coercive force available from such particles. Heretofore, a variety of attempts have been made to protect these magnetic particles from such oxidation including the method disclosed in the U.S. Pat. No. 4,558,077 noted above, as well as those disclosed in U.S. Pat. No. 3,933,536. All of these processes have attempted to coat the individual particles with an inert coating to prevent the oxidation of the magnetic particles. The U.S. Pat. No. 4,558,077 discloses a plurality of prior art processes for coating the magnetic particles and for bonding the particles together to form a magnet. That patent also discusses the problems associated with the prior art methods and proposes a new method of manufacturing magnets wherein the magnetic particles are mixed with a dry epoxy powder and then pressed to form the final magnet. While this process does provide some protection to the magnetic particles, it is not totally satisfactory since the final magnet may still exhibit loss of magnet coercivity upon exposure to the atmosphere.
The method of manufacturing a magnet disclosed in the U.S. Pat. No. 3,933,536 includes the mixing of the magnetic powder materials with a polymer and then precipitating the particles from the solution. However, as noted in the U.S. Pat. No., 4,558,077, it is believed that that method is unsuitable for producing the desired high density magnets since it does not remove all of the solvent from the precipitated polymers.
Still further, it has been found that the above processes of manufacturing magnets have resulted in the production of a wet paste containing the magnetic particles which requires further grinding to regenerate the particles necessary to form into the final magnet. It has been found that such regrinding strips a portion of the protective coating from the magnetic particles thereby exposing them to the atmosphere which adversely affects the magnetic properties of the final magnet.
Accordingly, the provision of a method for manufacturing epoxy bonded rare earth-iron magnets which provides adequate protection against oxidation or reactivity of the magnetic particles as well as the requisite compressed density of the particles would provide an extremely desirable magnet.